1. Field of the Invention
The present invention relates to an output method or an apparatus which uses an interface such as an RS-232C, SCSI or parallel interface such as that produced by the Centronics company.
2. Description of the Related Art
Recently, some printing devices have been developed which use interfaces and in which the device can change from one interface to another automatically. However, if one interface is selected, these printing devices can only receive data through the selected interface. Accordingly, there has developed a concept in which printing devices receive data simultaneously from several interfaces. However, in such devices, if they have fixed areas of memory corresponding to each interface as a receiving buffer, the total necessary memory area of the printing apparatus becomes a number of times larger than that necessary for devices that receive data through a selected interface. Furthermore, there are some printing devices using several interfaces, which can select the interface through which first data is received. For that reason, if a speed of transferring data through the selected interface is slow, the time necessary for receiving the data is long. Moreover, it is necessary for the device to interpret the received data and therefore, processing the data to be received through the unselected interfaces is still more delayed. Getting back to the device that selects the interface with which the first data is received as stated above. If the processing of the data is interrupted, such as, for example, at the middle of a page to be printed, processing the data to be received by the unselected interface is still more delayed. There are some devices with several interfaces including a two-way interface which can automatically change from one interface to another. But if one interface is selected, these printing devices can get and interpret data only through the selected interface.
So, there has been developed the concept of a printing device that receives data simultaneously through several interfaces. However, the data which can be interpreted is only the data which can be received through the selected interface. Even if host computers are provided to transfer the data to the printing device, the device can not get a status of affairs until the device selects the two-way interface.
In the above-described devices, error recovery is carried out for a selected interface or for all interfaces regardless of the reason for the error.
Furthermore, there are devices which can inform a user that a transmitting error has occurred. However, with such devices the incorrect data is still output after the error has occurred. In addition, there are devices that transfer busy signals and interrupt transferring of data. However, with which such devices after recovering from the error, the device begins to receive middle data.